The blown fiber technique is well known as involving the installation of optical fiber transmission lines into optical fiber tubes or ducts using the viscous drag provided a high-speed flow of a fluid medium (in practice, this is pressurized air from an air compressor), from EP 108590 and subsequent publications. In essence, plastic tubes or conduits are initially installed along paths or to locations where an optical fiber connection may one day be desired or necessary. The expensive decision to deploy optical fiber units (comprising a bundle of single fibers) along those paths can thus be deferred until a decision is made to have the fiber installed through the conduits by “blowing” them through.
The apparatus required for such an installation includes a blowing head and an air compressor. During installation, one end of the fiber tube is fitted to the blowing head, so that the bore of the tube communicates with a bore within the blowing head. Fiber unit and air is fed through the bore of the blowing head, into the bore of the tube. Thus the blowing head has two main functions: to mechanically drive the fiber unit into the tube, using a pair of drive wheels, and to direct pressurized air from the compressor into the tube via an air hose.
Currently, installing blown fiber requires at least two operators, for various reasons, such as the large size and sheer weight of the compressor in particular. The compressor currently used by the applicants weighs 85 kilograms (kg), which is impossible for a single person to lift. It is unwieldy, difficult and dangerous for a single person to remove it from a van even if mounted on a wheeled frame. This compressor, or one similar to it, is used by blown fiber practitioners in the UK and throughout the world, for example 6A Petrol Engine Driven Blown Fibre Compressor, the Sirocco Petrol Compressor (PRYSMIAN SPA [trade] S.p.A. of Milan, Italy), and so on.
The supplied air needs to satisfy certain criteria required for successfully blowing fiber. These include: Pressure, Volume, Temperature, Dryness, Oil carryover, and Smooth, pulse-free delivery, among others.
The air needs to flow within the tube at a sufficient velocity to provide the fluid drag to carry the fiber unit within the fiber tube. A discussion of air pressure and flow levels required for installing blown fibre can be found in EP 108590 (supra). It is desirable that a compressor for blown fiber installation deliver a smooth, pulse-free supply of air. The air should be relatively dry so that moisture from condensation should not interfere with the installation process, yet not so dry so that static electricity is generated by the movement of the fiber unit though the tube. As air temperature is related to air dryness, it is desirable that the air produced by the compressor should be not more then 2° C. above ambient.
As noted above, the pressurized air of this compressor is directed into the fiber tube via a bore within the blowing head. The blowing head typically comprises two parts clamped together, and more than half of the pressurized air pumped into the narrow bore of the blowing head escapes through the seams. As a result, installers typically need to use a large, powerful compressor capable of supplying the large quantity of air need to make up that wasted at the blowing head and which never reaches the tube. A typical compressor is capable of supplying up to 200 liters per minute.
The current blown fiber installation process is labor-intensive as requiring two operators, and the waste necessitates the use of larger and more powerful equipment than is perhaps strictly necessary. Installation costs are therefore high. Such expenditure was previously considered acceptable e.g. because optical fiber was to service high-worth commercial customers. Optical fiber is however becoming increasingly mass-deployed throughout networks worldwide. In the UK for example, a planned transition to a Next Generation Network (the BT “21ST CENTURY NETWORK”), and the move to “Fibre to the Kerb” or to the Home, all point to the increasing deployment of large volumes of optical fiber—for which blowing is an installation method of choice—throughout the network at a variety of levels. With this comes pressure to reduce costs, especially in the provisioning of optical connections to extremely price-sensitive residential customers.
In response, the applicants have developed an improved blowing head which decreases the level of wasted air, so that much more from the compressor may be delivered into the fiber tube. This is described in WO 2006103424, the disclosure of which is hereby incorporated by reference herein in its entirety. As a result of this improvement, a less powerful compressor can be used with the blowing head including the inventive feature described in WO 2006103424.
As a result, use of a compressor which is portable being small and light enough for a single operator to lift and safely deliver to the installation site, set up and manage, would contribute directly to potentially halving the manpower time and cost involved in an installation. Such a lightweight compressor would nonetheless need to reliably produce air of the industrial quality described above needed for a successful blown fiber installation.
Currently, compressors for industrial application which are capable of producing air to the required standard in a reliable manner for a successful installation exceed 25 kg, being the limit to what may be reasonably carried by a single operator. There are therefore severe design constraints in the arrangement of the essential components of a compressor suitable for the cost-efficient and widespread installation of blown fiber.